From: Park Heesob <phasis@...>
Date: 2004-11-13T10:21:39+09:00
Subject: Re: Win32, file descriptors and rb_io_check_writable()


Hi,
> 
> Hi all,
> 
> Windows 2000/XP
> VC++ 6.0 or 7.0
> Ruby 1.8.2 (Installer RC9)
> 
> I'm trying to write an extension for the win32-file package.
> Specifically, I want to write a wrapper for CreateFile() called
> File.nopen (for 'native open').  I thought this would be nice for two
> reasons.  First, it would give you finer control over HANDLE creation
> on the Win32 platform.  Second, it would allow you to open
> directories, since you cannot currently call File.open on a directory
> on Windows.
> 
> So, the API would look like this:
> 
> File.nopen(file, access, share, creation, flags)
> 
> The underlying C code looks like this:
> 
...
> For read operations, this works.  I can do this:
> 
> fh = File.nopen("C:\\somefile")
> p fh.readlines # works fine
> fh.close
> 
> 
> But, I cannot write to the filehandle:
> 
> fh = File.nopen("C:\\somefile")
> fh.puts "Hello"
> 
> test.rb:13:in `write': not opened for writing (IOError)
>        from test.rb:13:in `puts'
>        from test.rb:13
> 
> That error appears to be coming from the rb_io_check_writable()
> function, which in turn is checking the mode of the OpenFile struct
> defined in rubyio.h.
> 
> How do I deal with this?  Am I doing something wrong?  Or would it
> take a modification of io.c for this to work?  If so, what should be
> done?
> 
Following code will work:

#define OpenFile  WINAPI_OpenFile 
#include <windows.h>
...
#undef OpenFile 
#include "ruby.h"
#include "rubyio.h"
...
static VALUE file_nopen(int argc, VALUE *argv, VALUE klass){
   HANDLE h;
   int rv;
   VALUE args[1];
   VALUE rbFile, rbAccess, rbShare, rbCreation, rbFlags;
   DWORD dwAccess = FILE_ALL_ACCESS;  // I tried various flags here
   DWORD dwShare = FILE_SHARE_READ | FILE_SHARE_WRITE;
   DWORD dwCreation = OPEN_EXISTING;
   DWORD dwFlags = FILE_ATTRIBUTE_NORMAL;

   rb_scan_args(argc,argv,"14",&rbFile,&rbAccess,&rbShare,&rbCreation,&rbFlags);

   // Override default values with user supplied values
   if(Qnil != rbAccess)
      dwAccess = (DWORD)NUM2UINT(rbAccess);

   if(Qnil != rbShare)
      dwShare = (DWORD)NUM2UINT(rbShare);

   if(Qnil != rbCreation)
      dwCreation = (DWORD)NUM2UINT(rbCreation);

   if(Qnil != rbFlags)
      dwFlags = (DWORD)NUM2UINT(rbFlags);

   h = CreateFile(
      StringValuePtr(rbFile),
      dwAccess,
      dwShare,
      NULL,          // Cannot be inherited
      dwCreation,
      dwFlags,
      NULL           // No template
   );

   if(h == INVALID_HANDLE_VALUE)
      rb_raise(cFileError,ErrorDescription(GetLastError()));

   // Convert HANDLE to file descriptor
   args[0] = UINT2NUM(_open_osfhandle((long)h,O_RDWR));

   RFILE(self)->fptr->mode = rb_io_mode_flags("w+");                     //  mode string correspond to dwAccess 
   RFILE(self)->fptr->f = rb_fdopen(NUM2INT(args[0]),"w+");        //  mode string correspond to dwAccess 

   // Return a bonafide File object, based on the file descriptor
   return rb_class_new_instance(1,args,rb_cFile);
}

> Regards,
> 
> Dan
> 
>

Regards,

Park Heesob